Pressure sensors find utility in many devices, including pressure transducers, altimeters, depth measurement devices, switches, diaphragms, and the like. Pressure sensors also may be used in consumer electronic devices that utilize touch sensor pads or displays. Switches that rely on pressing a button or contact pad are well-known and often used in consumer electronic products to implement buttons. For example, various consumer electronic devices, e.g., a mobile telephone, a personal digital assistant, game controller, or remote controller, typically include a plurality of buttons that a user can press to invoke various operations with respect to such devices. Such buttons can, for example, be used for function (e.g., send, end, navigate, etc.) buttons or for buttons of an alphanumeric keypad/keyboard. These buttons in many cases are implemented by dome switches.
A dome switch typically consists of a dome made from metal that can be deformed temporarily by a user press to invoke a switching action. Then, when the user press is removed, the dome returns to its original, undeformed shape. Today, with many electronic devices, proper operation of buttons is an important requirement for usability and user satisfaction. With respect to dome switches, the tactile feedback provided by dome switches is often very helpful to users of the consumer electronic products. However, conventional assembly of such buttons implemented by dome switches is inefficient and complicated. Generally, a dome must be placed on a substrate and corresponding structures often provide a button or key structure (with or without an actuation nub) that can be pressed downward to engage the dome during a button or key press. In some designs, activation nubs are provided on the button or key structure or on the peaks of the domes themselves. The formation of the activation nubs is a separate manufacturing step that is tedious and time-consuming. In addition, the placement of the actuation nubs relative to the domes is not always as accurate as desired. For example, if the actuation nub does not properly align with the center region of a dome, the tactile feedback for such dome switch will be disturbed and therefore not as robust as intended.
Many such switches typically employ thin crystalline metal materials that can be deformed sufficiently to enable the switch to make contact and create a circuit. The material typically is a suitable conductor of electricity, thus enabling current to flow upon contact. Materials may be characterized by their Young's modulus E, also called elasticity modulus (generally expressed in GPa), which characterizes its resistance to deformation. Many materials also are characterized by their elastic limit σe (generally expressed in GPa), which represents the stress beyond which the material will plastically deform. Thus, it is possible, for a given thickness, to compare materials by establishing for each one the ratio of their elastic limit to their Young's modulus σe/E, wherein the ratio is representative of the elastic deformation of each material. The higher this ratio is, the greater the elastic deformation of the material.
Because switches on consumer electronic devices are operated frequently, the materials used to fabricate the switch must be capable of repeated deformation and return to their original configuration. The ability of a material to deform reversibly under stress is known as the material's elasticity. Above a certain stress, known as the elastic limit of a material or the yield strength, the metal material may deform irreversibly, becoming inelastic, exhibiting plasticity and adversely affecting the function and utility of the switch. Crystalline metallic materials such as those used in the prior art (e.g., titanium or stainless steel) typically have a low σe/E ratio. These crystalline materials therefore have a limited elastic deformation, and may after repeated use, ultimately fail.
Moreover, because this elastic limit is low, when it deforms it approaches its region of plastic deformation under low stresses with the risk that it cannot resume its initial form. To avoid such a deformation, the deformation of the membrane is restricted, i.e. the amplitude of the movement of the membrane is intentionally limited. Due to the nature of conventional switching systems, more deformable, non-crystalline materials are not practical. That is, the material that deforms in a conventional switch, makes contact with electrical connections to create a circuit. Non-conductive amorphous materials such as plastics and rubbers, which typically have much greater elasticity than most crystalline metal materials, therefore cannot be employed in conventional switching systems that rely on the application of pressure to a material, subsequent deformation of that material and then contact to create an electric current.
Pressure sensors measure pressure of gas or liquids, and typically operate by generating an electrical signal as a function of the pressure. Such pressure sensors often are referred to as pressure transducers, or pressure transmitters, pressure indicators, piezometers, manometers, and the like. These pressure sensors operate by making use of strain gauges attached to a deformable object, such as a diaphragm. As the diaphragm deforms, the strain gauge attached thereto deforms, thereby causing the electrical resistance of the gauge to change. The change in electrical resistance then can be measured using a Wheatstone bridge.